Racing vehicle game

ABSTRACT

A track for a racing car game is described. The width of the track is formed so as to exhibit an optically graded lateral profile that is maintained along the length of the track. The optically graded profile thus provides a means for allocating each lateral position of the track with a unique level of reflectivity. In this way the level of light reflected onto a detector from a vehicle associated light source corresponds to a unique lateral position, and thus provides a diagnostic for determining the lateral position of the vehicle on the track and for maintaining this lateral position along the full length of the track. The track may therefore be considered to comprise a plurality of virtual slots for the vehicle between which the vehicle can easily move and the choice of which is determined by the vehicle&#39;s operator.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of the earlier U.S. Utility patentapplication to Keating, et al. entitled “Racing Vehicle Game,” Ser. No.13/810,873, filed Mar. 26, 2013, now pending, which is a U.S. NationalStage Entry of International Patent Application No. PCT/GB2011/051365,filed Jul. 19, 2011, the disclosures of which are hereby incorporatedentirely herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to the field of racing vehicle games. Morespecifically, the present invention concerns methods for controlling theposition of a vehicle on a track so as to provide a slotless racingvehicle game.

2. State of the Art

Traditionally, racing vehicle games involve the racing of model slotcars. Each car comprises a guide peg (or swiveling blade) that isconfigured to locate within a guide slot within a track that acts todefine a lane for the car. Power for the car's low-voltage electricmotor is carried by metal strips located next to the slot and is pickedup by contacts located at the front of the car alongside the guide peg.The voltage used to power the car can be varied by an operator changinga resistance value within a corresponding hand controller.

It is known to also incorporate optional features such as brakingelements, electronic control devices and/or traction magnets to assistin the operation of the slot car. More recently, digital technology hasbeen developed which allows for more than one slot car to share a lane.

The challenge in racing slot cars comes in the taking of curves andother obstacles at the highest speed that will not cause the car to loseits grip and spin sideways, or to “de-slot”, leaving the track alltogether. Although, the actual model cars and tracks can accuratelyreplicate corresponding full scale vehicles and racing circuits therealism of racing model slot cars is severely limited by theinflexibility of the guide peg and the slots. Thus, unlike normalracing, variable positions across the width of a track cannot be adoptedby the operator of the model car in order to gain a tactical advantageor to protect a racing line. In addition, there is no facility withtraditional slotted tracks to incorporate additional racing hazards suchas oil slicks, gravel pits or variable weather conditions.

It is recognised in the present invention that considerable advantage isto be gained in the provision of a slotless racing vehicle game.

It is therefore an object of an aspect of the present invention toobviate or at least mitigate the foregoing disadvantages of the racingvehicle games known in the art.

SUMMARY

According to a first aspect of the present invention there is provided amethod for controlling the position of a vehicle on a track wherein themethod comprises the steps of:

taking a first measurement of a lateral position of the vehicle on thetrack;

comparing the first measured lateral position with a desired lateralposition for the vehicle so as to produce an error signal;

generating a first input signal for a steering servo of the vehicle soas to minimise the error signal;

measuring the speed of the vehicle;

employing the measured speed so as to compensate for speed dependentchanges in a response of the vehicle to an output signal from thesteering servo.

Preferably the step of taking the first measurement is carried out atthe front of the vehicle. This step may comprise employing an opticalsensor so as to measure light reflected from the track.

The step of measuring the speed of the vehicle may comprise measuringthe back emf generated by a motor employed to drive the vehicle.

The step of compensating for speed dependent changes in the response ofthe vehicle comprises varying the gain of a controller that generatesthe first input signal for the steering servo.

It is preferable for the gain of the controller to be varied with thereciprocal of the square of the speed of the vehicle. In an alternativeembodiment the gain of the controller is varied with the reciprocal ofthe square of the speed of the vehicle when the speed of the vehicle isabove a predetermined value.

The method for controlling the position of the vehicle on the track mayfurther comprise the step of measuring the angle between the directionof propagation of the vehicle and a longitudinal axis of the track.

The method for controlling the position of the vehicle on the track mayfurther comprise the step generating a second input signal for thesteering servo so as to minimise the measured angle.

The step of measuring the angle between the direction of propagation ofthe vehicle and a longitudinal axis of the track may comprise taking asecond measurement of a lateral position of the vehicle on the track.

Preferably the step of taking the second measurement is carried out atthe rear of the vehicle. This step may comprise employing an opticalsensor so as to measure light reflected from the track.

The step of measuring the angle between the direction of propagation ofthe vehicle and a longitudinal axis of the track may further comprisetaking the second measurement of the lateral position of the vehicle onthe track from the first measurement of the lateral position of thevehicle on the track.

According to a second aspect of the present invention there is provideda method for controlling the position of a vehicle on a track whereinthe method comprises the steps of:

taking a first measurement of a lateral position of the vehicle on thetrack;

comparing the first measured lateral position with a desired lateralposition for the vehicle so as to produce an error signal;

generating a first input signal for a steering servo of the vehicle soas to minimise the error signal;

measuring the angle between the direction of propagation of the vehicleand a longitudinal axis of the track; and

generating a second input signal for the steering servo so as tominimise the measured angle.

The error signal is preferably minimised within a primary feedback loopof the steering servo, the primary feedback loop having a firstresponsivity (Ks). The measured angle is preferably minimised within asecondary feedback loop of the steering servo, the secondary feedbackloop having a second responsivity (Klf2).

Preferably the second responsivity (Klf2) is equal to the reciprocal ofthe responsivity of the steering servo (Kss). Setting the secondresponsivity (Klf2) to be equal to the reciprocal of the responsivity(Kss) of the steering servo is found to significantly increase thestability of the positional control of the vehicle on the track.

Preferably the step of taking the first measurement is carried out atthe front of the vehicle. This step may comprise employing an opticalsensor so as to measure light reflected from the track.

The step of measuring the angle between the direction of propagation ofthe vehicle and a longitudinal axis of the track may comprise taking asecond measurement of a lateral position of the vehicle on the track.

Preferably the step of taking the second measurement is carried out atthe rear of the vehicle. This step may comprise employing an opticalsensor so as to measure light reflected from the track.

The step of measuring the angle between the direction of propagation ofthe vehicle and a longitudinal axis of the track may further comprisetaking the second measurement of the lateral position of the vehicle onthe track from the first measurement of the lateral position of thevehicle on the track.

The method for controlling the position of the vehicle on the track mayfurther comprise the step of measuring the speed of the vehicle.

Preferably the measured speed is employed to compensate for speeddependent changes in a response of the vehicle to an output signal fromthe steering servo.

The step of compensating for speed dependent changes in the response ofthe vehicle comprises varying the gain of a controller that generatesthe first input signal for the steering servo. This step may furthercomprise varying the gain of a controller that generates the secondinput signal for the steering servo.

It is preferable for the gain of feedback controller to be varied withthe reciprocal of the speed of the vehicle. In an alternative embodimentthe gain of a controller is varied with the reciprocal of the speed ofthe vehicle when the speed of the vehicle is above a predeterminedvalue.

Embodiments of the second aspect of the invention may comprise featuresto implement the preferred or optional features of the first aspect ofthe invention or vice versa.

According to a third aspect of the present invention there is provided amethod for controlling the position of a vehicle on a track wherein themethod comprises the steps of:

taking a first measurement of a lateral position of the vehicle on thetrack;

comparing the first measured lateral position with a desired lateralposition for the vehicle so as to produce an error signal;

generating a first input signal for a steering servo of the vehicle soas to minimise the error signal;

measuring the angle between the direction of propagation of the vehicleand a longitudinal axis of the track;

generating a second input signal for the steering servo so as tominimise the measured angle;

measuring the speed of the vehicle; and

employing the measured speed so as to compensate for speed dependentchanges in a response of the vehicle to an output signal from thesteering servo.

Embodiments of the third aspect of the invention may comprise featuresto implement the preferred or optional features of the first or secondaspects of the invention or vice versa.

According to a fourth aspect of the present invention there is provideda racing track suitable for racing one or more vehicles wherein theracing track comprises an optically graded lateral profile.

The optically graded profile thus provides each lateral position of thetrack with a unique level of reflectivity.

Preferably the optically graded lateral profile is maintained along alength of the track.

Most preferably the racing track comprises a closed loop track.

Preferably the optically graded lateral profile moves from regions oflow reflectivity at the inside of the track to regions of highreflectivity towards at the outside of the track.

The optically graded lateral profile may be greyscale, coloured orformed from an non-visible reflecting material e.g. an infra-redreflecting material.

The racing track may comprise paper with the optically graded lateralprofile printed thereon. As a result the racing track can be rolled upor folded for storage or transport purposes and then simply rolled outor unfolded as and when required.

The track may comprise separate track sections adapted to be fittedtogether. Such an embodiment allows for racing tracks of differentdesigns to be set up by a user through the reconfiguration of the tracksections.

The track may further comprise one or more markings. The markings may bedesigned to be read by an optical sensor, or to obscure the readingprocess of an optical sensor. In this way the markings facilitateadditional information e.g. lap times; to simulate hazards e.g. oilslicks, track debris, gravel pits; or to simulate changing handlingconditions requiring a vehicle to make a pit stop e.g. a vehiclepuncture or changing weather conditions.

According to a fifth aspect of the present invention there is provided acontrol circuit for controlling the position of a vehicle on a trackwherein the control circuit comprises:

a measurement sensor for measuring a first lateral position of thevehicle on the track;

a subtractor employed to produce an error signal by comparing the firstmeasured lateral position with a desired lateral position for thevehicle;

a controller for generating a first input signal for a steering servo ofthe vehicle so as to minimise the error signal;

velocity sensor for measuring the speed of the vehicle;

wherein the controller provides a means for employing the measured speedso as to compensate for speed dependent changes in a response of thevehicle to an output signal from the steering servo.

Preferably the control circuit further comprises a second measurementsensor for measuring the angle between the direction of propagation ofthe vehicle and a longitudinal axis of the track. In this embodiment thecontroller also generates a second input signal for the steering servoso as to minimise the measured angle.

Embodiments of the fifth aspect of the invention may comprise featuresto implement the preferred or optional features of the first and secondaspects of the invention or vice versa.

According to a sixth aspect of the present invention there is provided acontrol circuit for controlling the position of a vehicle on a trackwherein the control circuit comprises:

a measurement sensor for measuring a first lateral position of thevehicle on the track;

a subtractor employed to produce an error signal by comparing the firstmeasured lateral position with a desired lateral position for thevehicle;

a controller for generating a first input signal for a steering servo ofthe vehicle so as to minimise the error signal;

a second measurement sensor for measuring the angle between thedirection of propagation of the vehicle and a longitudinal axis of thetrack; and

wherein the controller generates a second input signal for the steeringservo so as to minimise the measured angle.

The first input signal for the steering servo is preferably generatedwithin a primary feedback loop of the steering servo, the primaryfeedback loop having a first responsivity (Ks). The second input signalfor the steering servo is preferably generated within a secondaryfeedback loop of the steering servo, the secondary feedback loop havinga second responsivity (Klf2).

Preferably the second responsivity (Klf2) is equal to the reciprocal ofa responsivity (Kss) of the steering servo. Setting the secondresponsivity (Klf2) to be equal to the reciprocal of the responsivity(Kss) of the steering servo is found to significantly increase thestability of the positional control of the vehicle on the track.

Preferably the control circuit further comprises a velocity sensor formeasuring the speed of the vehicle. In this embodiment the controlleralso provides a means for employing the measured speed so as tocompensate for speed dependent changes in a response of the vehicle toan output signal from the steering servo.

Preferably a variation of the gain of the controller when generating thefirst input signal provides the means for employing the measured speedso as to compensate for speed dependent changes in a response of thevehicle to an output signal from the steering servo. Similarly avariation of the gain of the controller when generating the second inputsignal provides the means for employing the measured speed so as tocompensate for speed dependent changes in a response of the vehicle toan output signal from the steering servo.

Preferably the gain of the controller is varied with the reciprocal ofthe speed of the vehicle.

Embodiments of the sixth aspect of the invention may comprise featuresto implement the preferred or optional features of the first and secondaspects of the invention or vice versa.

According to a seventh aspect of the present invention there is providea racing vehicle wherein the racing vehicle comprises a control circuitin accordance with the fifth aspect of the present invention.

According to an eighth aspect of the present invention there is providea racing vehicle wherein the racing vehicle comprises a control circuitin accordance with the sixth aspect of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

Aspects and advantages of the present invention will become apparentupon reading the following detailed description and upon reference tothe following drawings in which:

FIG. 1 presents a schematic representation of a vehicle in accordancewith an embodiment of the present invention;

FIG. 2 presents a block diagram showing the response of the vehicle ofFIG. 1 to steering commands;

FIG. 3 presents:

(a) a schematic representation of an optical sensor employed by thevehicle of FIG. 1; and

(b) an electronic circuit of the optical sensor;

FIG. 4 presents a plan view of an example racing track for the vehicleof FIG. 1;

FIG. 5 presents a block diagram showing a method employed to control theposition of the vehicle of FIG. 1 across the width of the track of FIG.4;

FIG. 6 presents a schematic representation of a vehicle in accordancewith an alternative embodiment of the present invention;

FIG. 7 presents a block diagram showing the response of the vehicle ofFIG. 6 to steering commands;

FIG. 8 presents:

(a) a first; and

(b) a second

block diagram showing a method employed to control the position of thevehicle of FIG. 6 across the width of the track of FIG. 4;

FIG. 9 shows a simplified block diagram of the method employed tocontrol the position of the vehicle of FIG. 6 across the width of thetrack of FIG. 4.

FIG. 10 presents a schematic representation of a vehicle in accordancewith an alternative embodiment of the present invention;

FIG. 11 presents a block diagram showing a first method employed tocontrol the position of the vehicle of FIG. 10 across the width of thetrack of FIG. 4; and

FIG. 12 presents a block diagram showing a second method employed tocontrol the position of the vehicle of FIG. 10 across the width of thetrack of FIG. 4.

DETAILED DESCRIPTION

FIG. 1 presents a schematic representation of a vehicle 1 in accordancewith an embodiment of the present invention. The vehicle 1 is shown on aracing track 2, further details of the track 2 being described belowwith reference to FIG. 4.

The vehicle 1 can be seen to comprise a main body 1 at the front ofwhich is mounted a set of steerable wheels 1 and to the rear of which ismounted a set of non-steerable wheels 1. Power for the vehicle isprovided via a dc electric motor 1 configured to drive the non-steerablewheels 5. A first controller unit 1, for example aproportional-integral-derivative controller (PID controller), provides ameans for an operator to remotely control the vehicle 1. A first opticalsensor 1 is positioned at the front of the vehicle 1 in order to providea means for determining the position of the vehicle 1 on the track 2. Avelocity sensor 1 is located at the non-steerable wheels 5 and isemployed to provide a means for measuring the speed of the vehicle 1.The steering angle (sa), and thus the direction of travel of the vehicle1, is controlled by a steering servo (s) 1 which is located within aclosed loop. The steering servo 10 exhibits a responsivity denoted byKss.

The way in which the position of the front of the vehicle (fp) acrossthe track 2 is affected by the input signal 1 to the steering servo (s)10 is represented by the block diagram 1 of FIG. 2. In particular, theinput signal 11 to the system (Input) is the signal fed to the steeringservo (s) 10 which may take a number of forms, for example an analoguevoltage, a pulse of certain width, or a binary number within amicrocontroller. The output signal 2 from the steering servo (s) 10represents the steering angle (sa) which results.

When an input signal 11 of a certain amplitude is applied to thesteering servo (s) 10 it causes the steerable wheels 4 to rotate to anangle relative to the body 3 of the vehicle 1. Thus, while the vehicle 1is moving forward at a certain speed (speed), the angle of the body 3 ofthe vehicle 1 to the track 2, the body angle (ba), will continuallyincrease. It will be appreciated that the longer the wheelbase (wb) ofthe vehicle 1, the smaller the effect of the steering angle (sa) willbe. Furthermore, the greater the speed at which the vehicle 1 istravelling the faster the body angle will change for a given steeringangle (sa). These aspects are represented by the various blockspresented in FIG. 2 as described in further detail below.

The output of the first sine block 2 is the sine of the input to thatblock, in other words it is the sine of the steering angle (sa). Theblock marked 1/wb 2 shows that the effect is inversely proportional tothe wheelbase (wb) of the vehicle 1. The fact that the steering angle(sa) is proportional to the speed of the vehicle 1 is shown by the firstmultiplier block 1, with speed being provided as a secondary input.Finally, the fact that a fixed steering angle (sa) causes the body angle(ba) to continually increase, indicates the presence of a time integralaction which is represented by the presence of the first, time integralblock 3.

Once the input signal 11 has returned to zero the steerable wheels 4will once more be aligned with the body 3 and so the body angle (ba)will remain at its current value. This non-zero value of the body angle(ba) will, however, cause the position of the front of the vehicle (fp)to continually increase. The rate of increase is once again proportionalto speed, and again it is the sine of the body angle (ba) that issignificant. These effects are shown by the remaining blocks of theblock diagram 12 of FIG. 2, namely the second sine block 3, the secondmultiplier block 3 and the second, time integral block 4.

Further details of the optical sensor 8 employed by the vehicle 1 arepresented in FIG. 3. In particular, FIG. 3( a) presents a schematicrepresentation of the optical sensor 8 while FIG. 3( b) presents anelectrical circuit for this component. The optical sensor 8 can be seento comprise a light source 3 in the form of an LED and a detector 3 inthe form of a phototransistor. Light 3 emitted by the light source 21 isinitially directed towards the track 2. Following reflection from thetrack 2 the light 23 is then incident upon the detector 22. As explainedin further detail below, the level of the light detected provides adiagnostic for measuring the position of the vehicle 1 across the widthof the track 2.

The following method may be employed to compensate the optical sensor 8for the effects of background light. The light source 21 may be turnedoff so as to allow a reading to be taken by detector 22. This readingcan be accounted for by the presence of ambient light. By subtractingthis reading from those recorded during the course of a race allows forthe effects of ambient light to be removed from the vehicle controlsystems described in further detail below.

The velocity sensor 9 provides a means for measuring the speed of thevehicle 1 by employing a technique whereby the back emf of the dcelectric motor 6 is measured. During normal operation the dc electricmotor 6 draws electrical energy and converts it into mechanical energyin order to drive the vehicle 1. When the power to the dc electric motor6 is interrupted the dc electric motor 6 acts as an electrical generatorand the above process is reversed i.e. the dc electric motor 6 takesmechanical energy and converts it into electrical energy. The voltageobserved when the dc electric motor 6 is operating as an electricalgenerator is directly proportional to the speed of the dc electric motor6. Thus by periodically interrupting the electrical supply to the dcelectric motor 6 (typically for a period of a few milliseconds) thevelocity sensor 9 can be used to measure the speed of the vehicle 1without significant disruption to the drive of the vehicle 1.

A remote control unit 1 provides an operator with the means forgenerating a command signal 1 for controlling the speed and lateralposition of the vehicle 1 on the track 2. In particular, the remotecontrol unit 24 comprises a throttle 1 which provides a means forgenerating a speed control component for the command signal 25 and asteering wheel 1, or joystick, which provides a means for generating atrack position component for the command signal.

Racing Track

A plan view of an example racing track 2 for the vehicle 1 is presentedin FIG. 4. In the presently described embodiment the racing track 2 canbe seen to form a closed loop. Reference to a longitudinal axis 1 of thetrack relates to an axis which extends around the length of the track,as illustrated by the dashed line presented in FIG. 4, while referenceto lateral movement of a vehicle 1 on the track 2 or lateral profilerefers to movement or a profile substantially perpendicular to thelongitudinal axis 28.

The width of the track 2 is formed so as to exhibit an optically gradedlateral profile that is maintained along the length of the track 2. Theoptically graded profile thus provides a means for allocating eachlateral position of the track 2 with a unique level of reflectivity. Inthe presently described example the optically graded lateral profilecomprises a greyscale profile (i.e. black to white) from the inside ofthe track 2 to the outside, so as to provide corresponding regions ofrelatively low reflectivity to high reflectivity for the light source 21of the optical sensor 8. In this way the level of light 23 reflectedonto the detector 22 from the light source 21 corresponds to a uniquelateral position and thus provides a diagnostic for determining thelateral position of the front of the vehicle (fp) on the track 2 andthereafter for maintaining this lateral position along the full lengthof the track 2.

It will be appreciated by those skilled in the art that the racing track2 need not necessarily comprise a greyscale, optically graded lateralprofile. The track may be formed from any suitable colour providing thatcorresponding regions of relatively low reflectivity to highreflectivity for the optical sensor 8 can be formed. Furthermore, thetrack 2 need not comprise a visible colour at all, but may instead beformed from an infra red reflecting material with a corresponding infrared light source 21 being employed within the optical sensor 8.

It is preferable for the track 2 to be formed by a printing processwhereby appropriate ink is applied to a thin paper. As a result theracing track 2 can be rolled up or folded for storage or transportpurposes and then simply rolled out or unfolded as and when required.

The track 2 may be printed on separate paper sections and then laid outas appropriate when required for a race to take place. Such anembodiment would allow for racing tracks 2 of different designs to beset up by a user through the reconfiguration of the track sections.

It will also be appreciated by those skilled in the art that additionalmarkings 1 may be incorporated within the track 2. These additionalmarkings 29 may be designed to be read by the optical sensor 8, or toobscure the reading process of the optical sensor 8, so as to facilitateadditional information e.g. lap timings; to simulate hazards e.g. oilslicks, track debris, gravel pits; or to simulate changing handlingconditions requiring a vehicle to make a pit stop e.g. a vehiclepuncture or changing weather conditions.

Velocity Sensor Control System

A closed loop control system 1 for controlling the position of thevehicle 1 on the track 2 will now be described with reference to theblock diagram of FIG. 5 and for a vehicle configured to travelanti-clockwise around the track 2.

The controller unit 7 is employed to receive the command signal 25 fromthe remote control unit 24. The speed control component of the commandsignal 25 is used to set the speed of operation of the dc electric motor6 and hence the speed of the vehicle 1 while the track positioncomponent is employed by the steering servo (s) to set a desired lateralposition for the first optical sensor 8 upon the track 2. For example,if the steering wheel 27 is in its zero position then the desired trackposition for the vehicle 1 is the centre of the track 2 and the vehicle1 follow the lateral axis 28 along the full length of the track 2. Ifthe steering wheel 27 is turned anticlockwise then a negative signal isgenerated which corresponding to a lateral track position closer to theinside of the track 2 i.e. a darker area of the track 2 which thevehicle 1 will then follows. Similarly, if the steering wheel 27 isturned clockwise then a positive signal is generated which correspondingto a track position closer to the outside of the track 2 i.e. a lighterarea of the track 2 for the vehicle 1 to then follow. The track maytherefore be considered to comprise a plurality of virtual slots for thevehicle 1 between which the vehicle 1 can easily move and the choice ofwhich is determined by the track position component of command signal25.

It will be appreciated by those skilled in the art that by inverting theabove arrangement the vehicles 1 can be configured to operate in aclockwise direction around the track 2. In a further alternativeembodiment, reversing the lateral graded shading of the track 2 wouldprovide for a clockwise racing configuration.

A first subtractor 1 is then employed in a primary feedback path 1 forthe steering servo (s) 10. The first subtractor 31 generates an errorsignal 1 that provides the input for the controller unit 7 bysubtracting a primary feedback signal from the track position componentof the command signal 25 and so allows for the controller unit 7 toprovide a diagnostic of the deviation of the first optical sensor 8 fromthe desired lateral track position. The responsivity of a sensor isgiven by the relationship between its input and its output. In thepresently described control system 30 the responsivity, denoted by Ks,is the relationship between the track positioned measured by the firstoptical sensor 8 and the output fed to the first subtractor 31. Onreceiving the error signal 33, the controller unit 7 then attempts todrive the steering servo (s) 10 so as to reposition the front of thevehicle 1 on the track 2 so as to minimise the error signal 33. In thisway the vehicle 1 will travel around the track 2 while trying tomaintain the lateral track position set by the track position component.If the track position component is changed then the vehicle 1 will thenattempt to reposition itself on the track 2 to the corresponding newlateral position.

As described above, the rate at which the body angle (ba) increases at agiven steering angle (sa) and the position of the front of the vehicle(fp) both depend on the speed of the vehicle 1. Thus the loop gain ofthe control system 30 depends upon the square of the speed of thevehicle 1. It is therefore extremely difficult to tune the controllerunit 7 of the control system 30 so as to give a fast and stable responsefor all vehicle 1 speeds. By way of example, a 1:20 scale vehicle 1employing a steering servo (s) 10 having a bandwidth of 10 Hz wouldtypically have a mid range speed of 1.5 ms⁻¹. Although the controlsystem 30 can be arranged to be stable at this speed of operation itsstability quickly deteriorates as the vehicle's speed moves above orbelow this mid-range value.

A solution to this problem is to employ the output of the velocitysensor 9 so as to modify the input to the steering servo (s) 10 from thecontroller unit 7 and thus compensate for the speed dependency of theforward path gain of the control system 30. The simplest modification isto make the gain of the controller unit 7 vary with the reciprocal ofthe square of the speed of the vehicle 1. This is achieved by employinga processor unit 1 connected between the velocity sensor 9 and thecontroller unit 7. It is noted however that this solution results invery high controller gains at low vehicle speeds.

In an alternative embodiment the processor unit 34 is employed to varythe gain of the controller unit 7 with the reciprocal of the square ofthe speed of the vehicle 1 only when the vehicle 1 is travelling above apredetermined minimum speed e.g. in the above provided example asuitable minimum speed would be 0.5 ms⁻¹.

Second Optical Sensor Control System

In the absence of a further control method the dynamics of the controlsystem 30 are set primarily by the response of the steering servo (s) 10and thus this system is effectively a forth order, type two system. Asis known to those skilled in the art such systems are not particularlystable, and so it can prove difficult for the control system 30 to keepthe vehicle 1 on the track 2, without further compensation. Analternative embodiment will now be described wherein further stabilitycompensation is achieved through the employment of a second opticalsensor located within the vehicle.

A vehicle 1 b that incorporates a second optical sensor is presentedschematically in FIG. 6. The vehicle 1 b can be seen to comprise many ofthe elements of the vehicle 1 presented in FIG. 1, namely: a main body3, a set of steerable wheels 4, a set of non-steerable wheels 5, a dcelectric motor 6, a controller unit 7, a first optical sensor 8positioned at the front of the vehicle 1 b, and a steering servo (s) 10.However, in the presently described embodiment a second optical sensor 8b is located at the rear of the vehicle 1 b. Also in the presentlydescribed embodiment there is no requirement for the velocity sensor 9.

FIG. 7 presents a block diagram 1 showing the response of the vehicle 1b of FIG. 6 to the command signal 25 generated by the remote controlunit 24. The response block diagram of FIG. 7 is similar to thatdiscussed above in connection with the response of the vehicle 1, and aspresented in FIG. 2, with the exception that an arm 1 representing theposition of the rear of the vehicle (rp) is now present.

A closed loop control system 1 for controlling the position of thevehicle 1 b upon the track 2 is presented by the block diagram of FIG.8( a) and the equivalent block diagram of FIG. 8( b). The controllerunit 7 is again employed to receive the command signal 25 from theremote control unit 24 so as to set the desired speed and position ofthe front of the vehicle 1 b on the track 2. The first subtractor 31 isagain employed in a primary feedback path 32 for the steering servo (s)10 so as to generate an error signal 33 which provides a diagnostic ofthe deviation of the front of the vehicle 1 from the desired position.The responsivity of on the primary feedback path 32, is again denoted byKs.

In addition, the control system 37 employs a secondary, or local,feedback path 1 to the steering servo (s) 10. The secondary feedbackpath 38 provides a second subtractor 1 located therein with the measuredposition of the rear of the vehicle (rp). The second subtractor 39 isconfigured to then provide a secondary feedback signal to the steeringservo (s) 10 that equals the difference between the front and rearpositions of the vehicle, namely (fp)−(rp).

With reference to FIG. 6, basic trigonometry shows us that thedifference between the front (fp) and rear positions (rp) of the vehicle1 b on the track 2 is given by the sensor base (sb) multiplied by thesine of the body angle, or put another way:

((fp)−(rp))=(sb)·sin(ba)  (1)

Therefore, by measuring the front (fp) and rear positions (rp) of thevehicle 1 b on the track 2, and calculating the difference between thesevalues, allows for a secondary feedback signal to the steering servo (s)10 that is dependent upon the body angle (ba), rather than just thesteering angle (sa). The secondary feedback loop thus acts to minimisethe measured body angle so as to keep the vehicle 1 b travellingparallel to the longitudinal axis 28 of the track 2.

In addition, since the first time integral block 17 is now containedwithin the secondary feedback loop this has the effect of convertingthis block so as to act as an exponential lag rather than a timeintegration. The control system 37 can therefore be considered a forthorder, type one system which, as appreciated by those skilled in theart, is significantly more stable than a fourth order, type two system.Furthermore, the control system 37 also reduces the effects of speed onthe stability of the system 37 since the part of the system that has again which changes with speed is now contained within the local feedbackloop.

It will also be appreciated by those skilled in the art that both thesteering angle (sa) and body angle (ba) will be typically 30° or less.As a result a further simplification to the control system 37 can bemade by exploiting the fact that for small angles θ, sin(θ) isapproximately equals to θ. A simplified effective control system 37 a istherefore presented by the block diagram of FIG. 9 wherein the first 14and second 18 sine blocks are omitted.

In practice, it is found to be preferable for the stability of thecontrol systems 37 and 37 a if the responsivity on the of the secondaryfeedback path 38, Klf2, is made to be equal to the reciprocal of theresponsivity (Kss) of the steering servo (s) 10. Together with thenegation in the second subtractor 39 this results in the steering angle(sa) being set equal and opposite to the body angle (ba). The secondaryfeedback loop 38 thus makes the steerable wheels 4 point in thedirection that the vehicle 1 b should be travelling.

In the absence of the secondary feedback loop, if the front position ofthe vehicle (fp) were at the correct position, but the vehicle were atan angle to the track 2 then as soon as the vehicle 1 b moved forwardthe front position of the vehicle (fp) would deviate from the desiredposition before the overall feedback eventually brought it back intoline. With the addition of the second sensor 8 b at the rear of thevehicle 1 b and the secondary feedback path 38 the steerable wheels 4are automatically pointed along the track 2 and as the vehicle 1 b movesforward the rear position (rp) simply follows the front position (fp) tothe correct position across the track 2. Thus it can be considered thatthe control systems 37 and 37 b anticipate the impending positionalerror of the vehicle 1 b and then takes the necessary action to correctthis positional error before it occurs.

Velocity Sensor and Second Optical Sensor Control System

In a preferable alternative embodiment the control system for thevehicle employs a combination of both of the above described controlsystems 30 and 37. By way of example, FIG. 10 presents a vehicle 1 cthat incorporates both the velocity sensor 9 and the second opticalsensor 8 b. The remaining elements of the vehicle 1 c correspond tothose presented in FIG. 1 and FIG. 6 in connection with the previouslydescribed vehicles 1 and 1 b and are thus marked with correspondingreference numerals.

A first closed loop control system 1 for controlling the position of thevehicle 1 c upon the track 2 is presented by the block diagram of FIG.11. As with the previously described systems 30 and 37, the controllerunit 7 is employed to receive the command signal 25 from the remotecontrol unit 24 so as to set the desired speed and position of the frontof the vehicle 1 c on the track 2. The first subtractor 31 is thenemployed in a primary feedback path 32 to the steering servo (s) 10 soas to generate an error signal 33 which provides a diagnostic of thedeviation of the front of the vehicle 1 from the desired position. Theresponsivity of the primary feedback path 32, is again denoted by Ks.

The secondary, or local, feedback path 38 again provides details of theposition of the rear of the vehicle (rp) to the second subtractor 39located between the first controller unit 7 and the steering servo (s)10. The second subtractor 39 is again configured such that the secondaryfeedback loop acts to minimise the measured body angle of the vehicle 1c on the track 2. The responsivity of the secondary feedback path 38,Klf2, is again preferably made to be equal to the reciprocal of theresponsivity (Kss) of the steering servo (s) 10. In order to provide ameans for implementing velocity compensation within the secondaryfeedback loop it should be noted that a second controller unit 7 b islocated between the second subtractor 39 and the steering servo (s) 10.

In the presently described embodiment the gain of the primary feedbackloop and the secondary feedback loop are modified by the controllerunits 7 and 7 b so as to vary with the reciprocal of the speed of thevehicle 1 c, rather than the reciprocal of the speed squared, as wasrequired within the control system 30. This is however achieved in asimilar manner, namely by employing processor units 34 and 34 bconnected between the velocity sensor 9 and the first and secondcontroller units 7 and 7 b, respectively.

In an alternative embodiment the processor units 34 and 34 b may be isemployed to vary the gain of the primary and secondary feedback loopsvia the controller units 7 and 7 b, respectively, with the reciprocal ofthe speed of the vehicle 1 c only when the vehicle 1 c is travellingabove a predetermined minimum speed.

A second control system 11 for controlling the position of the vehicle 1c upon the track 2 is presented by the block diagram of FIG. 12. Thisembodiment is similar in many respects to the control system 40presented in FIG. 11 and discussed in detail above. The one significantdifference is that the second controller unit 7 b is omitted such thatthe variation of the gain of the secondary loop is carried within thefeedback path 38 itself. This is a less preferable solution since itrequires different processing for the forward path controller 7 aschanging the feedback path gain of the secondary feedback path 38changes the closed loop response of the secondary loop, and thus changesthe loop gain of the primary loop.

It will be appreciated by those skilled in the art that all in of thedescribed embodiments the vehicles the steering servo may be adaptedsuch that instead of varying the angle of the steerable wheels a changein direction of the vehicle is achieved by varying the relative rotationof the wheels.

Furthermore, it will be appreciated that although the controller units 7and 7 b, subtractors 31 and 39 and the processor units 34 and 34 b haveall been presented as separate units their functionality may beimplemented directly with a single controller unit.

The racing vehicle game describe above offers many advantages over thosegames known on the art. In the first instance a slotless track andvehicle combination is provided whereby the lateral position of avehicle can be varied such that it can move across the full width of thetrack. This provides a more realistic racing vehicle game since theoperator of the vehicle can manoeuvre it in order to gain a tacticaladvantage (e.g. to overtake or nudge an opponent or to protect a racingline) but without having to steer the car around the track.

Secondly, if a vehicle does comes off of the track it can simply bedriven back on and the operation of the control system for the vehicleon the track resumes. Thus, unlike slot cars there is no need for anoperator to physically reposition their vehicle on the track in orderfor racing to resume.

The track itself also offers a number of significant advantages. In thefirst instance there is no limit to the number of vehicles that may beraced since there are no predetermined slots required for the operationof a vehicle. The track is highly flexible allowing for simple storage,transportation and deployment. The track is simple to produce and sosignificantly more cost effective than traditional slotted tracks knownin the art. Finally the track allows for the incorporation of additionalracing hazards such as oil slicks, track debris, gravel pits or variableweather conditions.

A method and apparatus for controlling the position of a vehicle on atrack so as to provide a slotless racing vehicle game is described. Themethod involves measuring the lateral position of the vehicle on thetrack so as to minimise the distance with a user defined lateralposition. A measured velocity of the vehicle is then feedback to asteering servo in order to stabilise the vehicle's position at thedesired lateral position. In particular, the gain of a controller thatgenerates the input signal for the steering servo is varied with thereciprocal of the square of the speed of the vehicle.

The foregoing description of the invention has been presented forpurposes of illustration and description and is not intended to beexhaustive or to limit the invention to the precise form disclosed. Thedescribed embodiments were chosen and described in order to best explainthe principles of the invention and its practical application to therebyenable others skilled in the art to best utilise the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated. Therefore, further modifications orimprovements may be incorporated without departing from the scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A racing track suitable for racing one or more vehicles wherein the racing track comprises an optically graded lateral profile.
 2. A racing track as claimed in claim 1 wherein the optically graded profile provides each lateral position of the track with a unique level of reflectivity.
 3. A racing track as claimed in claim 1 wherein the optically graded lateral profile is maintained along a length of the track.
 4. A racing track as claimed in claim 1 wherein the racing track comprises a closed loop track.
 5. A racing track as claimed in claim 1 wherein the optically graded lateral profile moves from regions of low reflectivity on a first side of the track to regions of high reflectivity towards on a second side of the track.
 6. A racing track as claimed in claim 1 wherein the optically graded lateral profile is greyscale, coloured or formed from an non-visible reflecting material.
 7. A racing track as claimed in claim 1 wherein the racing track comprise paper with the optically graded lateral profile printed thereon.
 8. A racing track as claimed in claim 1 wherein the track comprises separate track sections adapted to be fitted together.
 9. A racing track as claimed in claim 1 wherein the track further comprises one or more markings.
 10. A racing track as claimed in claim 9 wherein the markings are designed to be read by an optical sensor, or to obscure the reading process of an optical sensor.
 11. A racing track as claimed in claim 9 wherein the markings facilitate one or more additional information for the racing track from the set of additional information comprising lap times, oil slicks, track debris, gravel pits or changing handling conditions. 